Objective: Gastric cancer (GC) is one of the most common human cancers. A useful method of gastric cancer stem cell (CSC) characterization is spheroid colony formation. Previously, we reported that KIF11 expression is >2-fold in spheroid-body-forming GC cells compared with parental cells. Here, we analyzed the expression and distribution of KIF11 in human GC by immunohistochemistry. Methods: Expression of KIF11 in 165 GC cases was determined using immunohistochemistry. For mucin phenotypic expression analysis of GC, immunostaining of MUC5AC, MUC6, MUC2 and CD10 was evaluated. RNA interference was used to inhibit KIF11 expression in GC cell lines. Results: In total, 119 of 165 GC cases (72%) were positive for KIF11. Expression of KIF11 was not associated with any clinicopathologic characteristics; however, it was observed frequently in GC exhibiting an intestinal phenotype. Both the number and size of spheres formed by MKN-74 cells were significantly reduced following transfection of KIF11-targeting siRNA compared with negative-control siRNA. Furthermore, levels of phosphorylated Erk1/2 were lower in KIF11 siRNA-transfected cells than with negative-control siRNA-transfected cells. Conclusion: These results indicate that KIF11 is involved in intestinal mucin phenotype GC.

Gastric cancer (GC) is one of the most common human cancers. Genes expressed only in cancer tissue, especially on the cell membrane, may be useful biomarkers for cancer diagnosis and therapeutics. In the present study, we focused on the PCDHB9 gene, which encodes the transmembrane protein protocadherin B9. Immunohistochemical analysis revealed that 62 (36%) of 173 GC cases were positive for protocadherin B9. Protocadherin B9 staining was mainly observed on the GC cell membrane. Expression of protocadherin B9 was frequently found in intestinal-type GC and correlated with poor prognosis in patients with intestinal-type GC. Although PCDHB9 knockdown or forced expression of PCDHB9 did not change cell growth or invasion activity in a GC cell line, cell adhesion to fibronectin was significantly reduced by PCDHB9 knockdown and significantly enhanced by overexpression of PCDHB9. Expression levels of ITGA3, ITGA4, ITGA5, and ITGB1 were significantly reduced by knockdown of PCDHB9 and significantly enhanced by overexpression of PCDHB9. Furthermore, both the number and the size of spheres in culture were significantly decreased by PCDHB9 knockdown and significantly increased by overexpression of PCDHB9. In a peritoneal dissemination mouse model, the weight of the total disseminated nodules of MKN-74 cells was significantly increased by forced expression of PCDHB9. These results indicate that protocadherin B9 plays an important role in the progression rather than the pathogenesis of intestinal-type GC. Specific inhibitors of protocadherin B9 may constitute promising anti-cancer drugs with fewer side-effects. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Abstract. Background: Oesophageal squamous cell carcinoma (ESCC) and colorectal cancer (CRC) are common types of human cancer. Spheroid colony formation is used to characterize cancer stem cell (CSCsGastrointestinal (GI) cancer, including oesophageal squamous cell carcinoma (ESCC), gastric cancer (GC), and colorectal cancer (CRC), are common malignancies worldwide. A variety of genetic and epigenetic alterations are associated with GI cancer, and better knowledge of the changes in gene expression that occur during gastric carcinogenesis may lead to improvements in diagnosis, treatment, and prevention (1). Genes encoding transmembrane/secretory proteins that are specifically expressed in cancer are ideal diagnostic biomarkers. Moreover, if the gene product functions in the neoplastic process, the gene is not just a potential biomarker, but may also be a therapeutic target (2).In the past decade, cancer has been recognized as a stem cell disease (3). Cancer stem cells (CSCs) are defined as malignant cells that possess the ability to initiate tumour growth and sustain self-renewal (4). Moreover, CSCs play an important role in resistance to chemotherapy (4). Therefore, characterization of CSCs is important for establishing more effective cancer treatments. One useful method for characterizing CSCs is spheroid colony formation. We previously showed that KIF11 and kinesin family C1 (KIFC1) genes are more highly expressed, by more than two-fold, in spheroid-forming cells than in the parental cells of GC cell lines (5). We also showed that KIF11 protein expression is upregulated in GC tissue samples, and that both the number and size of spheres produced by GC cells are significantly reduced by inhibition of KIF11 (6). These results suggest that KIF11 likely plays an important role in gastric CSCs.KIF11 (also known as EG5) is a member of the kinesin superfamily. The kinesin superfamily proteins are classified as mitotic kinesins, which are involved in cell division, and non-mitotic kinesins, which are principally involved in intracellular transport (7). KIF11 is a mitotic kinesin and is required for the separation of duplicated centrosomes during spindle formation (8). Thus, a KIF11 inhibitor is thought to be useful to specifically target proliferating tumour tissue (9). Several small molecule KIF11 inhibitors have been reported (10). There is a possibility that KIF11 inhibitors 47